A valve spring retainer for engine acts to receive an end of a valve spring, and retain intake/exhaust valves and a cotter fitted in the valves, which are located inside the retainer, so that the valve spring does not unfasten during operation of the valves.
JP-A-7-180013, for example, proposes a valve spring retainer for engine using a Ti-6Al-4V-based Ti alloy as a material. The valve spring retainer is now described with reference to FIG. 11 hereof.
As shown in FIG. 11, the valve spring retainer for engine 200 has a through-hole 201 through which valves aligned along an axis pass, and receiving parts 202, 203 for supporting the valve spring at a periphery of the through-hole.
JP-A-7-180013 discloses a technique for hot-forming the Ti-6Al-4V-based Ti alloy at 300 to 800° C. into a certain shape.
Furthermore, JP-A-7-180013 discloses a technique for cold-forming a Ti-4Al-22V-based Ti alloy at about 200° C. into a certain shape.
However, the Ti-6Al-4V-based α/β Ti-alloy has the problem that since it must be formed by hot forging, finishing is necessary to improve dimension accuracy or obtain a smooth surface, which increases production cost due to increase in number of steps and the like.
On the other hand, the Ti-4Al-22V-based Ti alloy is a β-type Ti alloy, which is formed by cold rolling, and therefore a product with excellent shape is obtained. However, the β-type Ti alloy has the problem that the material is expensive, and that the life of the metal mold is short because of high deformation resistance in forging, resulting in increase in cost of the valve spring retainer for engine.